Silicon carbide (hereinafter, also represented as SiC) has drawn attention as a material for a next-generation power semiconductor device. SiC has breakdown electric field strength approximately ten times higher than silicon (hereinafter, also represented as Si) as well as thermal conductivity approximately three times higher than Si, and is capable of realizing a low-loss power semiconductor device operable at a high temperature, which is difficult to be realized by a Si power device.
For example, a high breakdown voltage power MOSFET has low on-resistance and a high breakdown voltage, and is also capable of realizing fast switching. Therefore, it is widely used as a switching element of a power circuit such as a switching power supply. The high breakdown voltage power MOSFET has a vertical MOSFET structure in which a source electrode, a gate electrode, and a well electrode are formed on a surface of a substrate, and a drain electrode is formed on a back surface of the substrate. Further, a double-implantation MOSFET (hereinafter, also represented as DIMOSFET) structure in which a channel forming region (well region) and a source region are formed on a surface of a substrate using ion implantation is an excellent device structure in which a channel region can be simply and accurately formed, and is also suitable for a parallel operation.
Although the high breakdown voltage power MOSFET is a suitable device for a high-speed operation, the fact that the gate electrode has high resistance is a technical problem for the realization of the high-speed operation when a DIMOSFET using a SiC substrate is formed. To realize the high-speed operation of the device, it is necessary to reduce the resistance of a poly-Si gate electrode. Therefore, typically, a silicide having low resistance is formed by an interfacial solid-phase reaction with a metal on an upper portion of the poly-Si.
However, there is a difference in process temperature for the formation of the silicide between on the polycrystalline silicon of the gate electrode and on the SiC substrate of the source electrode. Therefore, the formation of the silicide on the polycrystalline silicon and on the SiC substrate cannot be performed simultaneously. More specifically, in a case of the formation of a nickel silicide having a small specific resistance, a thermal process temperature required for the formation of the silicide of the source electrode is 650° C. or more. On the other hand, the nickel silicide on the polycrystalline silicon of the gate electrode causes an aggregation of a film in the thermal process of 650° C. or more, and therefore a gate electrode having sufficient low resistance cannot be formed due to an increase of sheet resistance of the gate electrode.
Further, a layered structure of the polycrystalline silicon and the nickel silicide may raise a concern of increasing the sheet resistance during a device operation under a high-temperature environment, and has also reliability concern.